Readme and cleanup

src/vector.S

@@ -16,6 +16,8 @@ vector_table:
 
     ventry .
     ventry irq_handler     // IRQ(Interrupt Request) 0x280
+    ventry .
+    ventry .
 
 
 .align 4
@@ -25,26 +27,23 @@ el2_to_el1:
 
     mov x0, #(1 << 31)
     msr HCR_EL2, x0
-    isb
 
-    // Set SPSR_EL2: return to EL1h (EL1, using SP_EL1)
+    // Set SPSR_EL2: return to EL1h
     mov x0, #(0b0101)
     msr SPSR_EL2, x0
-    isb
 
     // Set return address to ELR_EL2
     ldr x0, =kernel_main
     msr ELR_EL2, x0
-    isb
 
     // Set SP_EL1 to stack base
     ldr x0, =__stack_end
     msr SP_EL1, x0
-    isb
 
     // Set VBAR_EL1 to vector table
     adr x0, vector_table
     msr VBAR_EL1, x0
+
     isb
 
     // Return to EL1